A.Jackson Avro Aircraft since 1908 (Putnam)

Avro 521

Designed late in 1915, the Avro 521 two seat fighter-trainer was a hybrid embodying the features of several Avro 504 variants. In side elevation the straight top longerons proclaimed it a derivative of the 504 prototype, yet the short span ailerons and the rudder/tail skid assembly were pure 504A, the cockpit positioning and centre section struts were 504E, the Vee strut undercarriage was contributed by the 504G and the streamlined headrest was copied from the Avro 519. Standard Avro 504 mainplanes were shortened to a span of approximately 27 ft. 6 in., cut away at all four wing roots to improve upward and downward vision and rigged with only a single set of interplane struts on each side. The engine was a 110 h.p. Clerget rotary in characteristic Avro cowlings. The initial order was for one machine, test flown at Trafford Park, Manchester by F. P. Raynham with H. E. Broadsmith standing up in the rear cockpit and brandishing a dummy machine gun to enable the effect of the extra drag to be assessed. Raynham found the Avro 521 longitudinally unstable and unpleasant to fly; nevertheless it was delivered to Farnborough in February 1916 and 25 production machines were ordered for the R.F.C. Proposals were also made for interchangeable wings to suit different roles but it is not known if any aircraft were actually modified. Designation Avro 521A was allotted to a version with mainplanes of 46 ft. span, while with standard Avro 504 mainplanes of 36 ft. span it was to have been known as the Avro 521B. It is doubtful if all were completed and there is no record of any production Avro 521 having been delivered. This strengthens the belief that the Avro 521 in which Capt. Garnett crashed and was killed at Gosport in 1917 must have been the prototype.

SPECIFICATION AND DATA Manufacturers: A. V. Roe and Co. Ltd., Clifton Street, Miles Platting, Manchester Power Plant: One 110 h.p. Clerget Production: One unmarked prototype Works Order number believed 1811; and twenty-five production aircraft 7520 to 7544, believed not all built Service Use: At the Advanced Training School, Gosport, Hants.

H.King Armament of British Aircraft (Putnam)

521. Designed in 1915 as a two-seat 'fighting scout#, the 521 (completed 1916) was intended to have a rear-mounted Lewis gun, though this does not appear to have materialised.

W.Green, G.Swanborough The Complete Book of Fighters

AVRO 521 UK

The Avro 521 two-seat fighter, which was flown late in 1915, was something of a hybrid in that it embodied a number of Avro 504 components. Powered by a 110 hp Clerget 9Z nine-cylinder rotary, the prototype had provision for a free-mounted 0.303-in (7,7-mm) Lewis gun fired from the rear cockpit. The prototype underwent official trials early in 1916, and 25 aircraft were ordered for the RFC, but this contract was subsequently cancelled, and there is no evidence that any Avro 521 other than the prototype (which crashed at Upavon on 21 September 1916) was built.